Elongated, flexible guide wires are often used in medical procedures to gain access to specific inner areas of the body without major surgery. Guide wires may be passed into the body via peripheral blood vessels, the gastrointestinal tract, or the urinary tract, and when in place may be used to guide catheters and the like into place.
A common method used to insert catheters in the human body is the percutaneous Seldinger technique. According to this method, a hollow introducer needle is inserted into a desired blood vessel under topical anesthesia. After the needle is properly placed, which may be indicated by the passage of blood through the needle, a guide wire is passed through the needle and into the vessel. Once the guide wire is in place, the needle is retracted and a catheter is introduced over the wire, the guide wire being used to maneuver the catheter to the desired point in the cardiovascular system. This point may be close to the area of insertion into the vessel, such as where the guide is simply used to introduce a catheter for intravenous fluid supply, or it may be far removed from that area, as when the guide is used in angiocardiographic applications. Once the catheter is in place, the guide is removed and the next step of the medical procedure may proceed.
To facilitate threading a guide through a predetermined body channel such as an artery, the guide may include a generally flexible body portion which is resistant to kinking and a forward end portion of increased flexibility, the end portion terminating in a smoothly rounded tip. The body portion may include a core of stainless steel or other metal, the core being appropriately dimensioned in cross section to provide the desired degree of flexibility to the guide wire.
To provide greater flexibility to the guide at its forward end, and provide radio opaqueness, a flexible length of helically wound wire forming an elongated coil is often employed at the forward end of the guide wire for this purpose. In this situation, a small plug commonly is employed at the forward end of the coil to provide the guide with a smoothly rounded tip and to restrain separation of the coil from the remainder of the wire when the guide wire is withdrawn, the plug being welded (including soldering or brazing) to the forward end of the core wire or to the forward end of a safety wire lying along the core wire. However, the forward plug may separate from the core or safety wire, making it difficult to extract the plug and the wire coil from the blood vessel into which it had been introduced. Also, leading coil lengths can become snagged on the distal end of a needle. Another difficulty with external helical coils is that there are practical limits to the coil diameter which may preclude the practical use of such wires in pediatric care where smaller blood vessels are encountered. U.S Pat. No. 4,619,274 describes a guide unit with an external helical coil having a forward end of sufficiently attenuated diameter so that it may be used in smaller vessels, the desired diameter being laboriously obtained by welding together a series of coils of progressively smaller diameters into a single coil of sequentially decreased diameter.
Unfortunately, the attachment via weldments of safety wires or core wires to forwardly positioned buttons in guide wires of the type described is not particularly strong. Moreover, several manufacturing steps are required, driving up the cost of these devices. It appears that failure occurs generally in the weldment between the forward end of the safety wire or core wire and the metal plug or button at the forward end of the guide wire, and this problem is particularly severe when the core wire or safety wire is made of a shape memory alloy such as nitinol. It would be desirable to provide a flexible guide having a forward tip which is far more securely fastened to the body of the guide, and further to provide a flexible guide with a small diameter that avoids the expense and weakened weldment joints necessitated by forming a helical coil from a series of independent wires.